This invention relates to a drive sprocket for a saw chain, wherein the sprocket has pockets for receiving the drive tangs on the saw chain and debris-clearing openings associated with the pockets which are wider than remainder portions of the pockets to allow debris to clear radially therefrom.
Chain saws generally comprise four major components; an endless saw chain, an elongate bar to support the chain around the edges of which the chain is trained for travel, power drive means in the form of a motor, and means including a sprocket to drivingly connect the shaft of the motor to the saw chain. The saw chain generally has opposed side links, interposed between which are drive links pivotally connected thereto with drive tangs extending below the bottom surfaces of the side links. Sprockets, generally referred to as rim sprockets, are known which have drive tang-receiving pockets of such depth and width that most of the bottom surfaces of the side links rest against and are supported by the peripheral edges of the rim portion of the sprocket. In the past such pockets have been of substantially constant width throughout the length of the pocket.
A problem accompanying chain saw use is the collection of chips and other debris or foreign matter in the pockets of such drive sprockets. Such matter is carried by the chain into the pockets, and eventually accumulates therein unless there is some clearing means. If the debris builds up in the pocket, it can be detrimental to the chain and other parts of the equipment. For instance, as debris piles up in a pocket, it prevents the chain from seating properly on the sprocket which increases the tension in the chain as it is driven around the sprocket and bar. It also may lift the drive links from the periphery of the sprocket producing instability as the chain travels about the sprocket.
In chain saws with automatic sharpening devices positioned adjacent the sprocket, buildup of debris, chips, and other foreign matter in the pockets of the sprocket can produce uneven sharpening. Explaining further, the sharpening apparatus adjacent the sprocket is positioned to engage the tops of cutter links in the chain as they are carried in an arc about the sprocket. The sharpening means is held in a selected position spaced radially outwardly from the sprocket to grind the tops of the cutter links. Should an individual pocket be impacted with excess chips or other foreign matter it can cause the cutter link adjacent the drive link in that pocket to be shifted radially outwardly a distance farther from the sprocket than other cutter links, resulting in uneven sharpening, and possibly damage to the chain or sharpening equipment.
A general object of the present invention is to provide a novel sprocket having means permitting effective radial clearing of chips and other foreign matter from the sprocket while still fully supporting the side links of the chain.
A more specific object of the present invention is to provide a drive sprocket for a chain saw in which clearance ports open radially to the periphery of the sprocket and are so positioned relative to a chain trained on the sprocket that they open into regions between leading and following side links in the chain to allow debris to exit radially from the sprocket.
Yet another object of the present invention is to provide such a novel sprocket in which drive tang-receiving pockets on the sprocket have widths through a major portion of their length which are only slightly greater than the width of a drive tang on the chain to provide stability for the chain as it is driven by the sprocket, and have clearance openings which are a minor portion of the length of the associated pocket but have greater width than remainder portions of the pocket.
A still further object of the invention is to provide such a novel sprocket in which a clearance opening diverges substantially continuously on progressing radially outwardly toward the periphery of the sprocket.